Office chairs normally include a vertical adjustment for the chair backrest. Such back adjust devices allow for limited movement of the backrest up and down on the back upright of a chair. Many such devices are difficult to operate as it often requires the release of a locking pin secured within a notched slot or similar arrangement in which a pin must be disengaged and engaged in the notches of the slot. These arrangements provide for a limited number of preset backrest positions. The present invention provides a mechanism for easy vertical adjustment and securement of a chair backrest and allows placement of the backrest in an infinite number of positions.